Treatment of viscose products



Kafka/fan Fae/0r //1 72/7773 of Maj/maria? Oxide Feb. 12, 1952 H. J. LESSER' 2,585,141

TREATMENT OF VISCOSE PRODUCTS Filed Sept. 5, 1945 2 Sl-IEETS-Sl-IEET 2 Q80 J J 400 450 00 JJ'O 660 6.5' INVENTOR 'ATTORNEYS Patented Feb. 12, i952 UNITED STATES ATENT QFFHCE TREATMENT or viscosE rn'onno'rs- Herman Joseph Lesser, Rome; Ga.,

assignor, by

mesne assignments, to Celanese Corporation of America, a corporation of Delaware Application September 551945, Serial No. 614,579

20 Claims.

1 This invention relates to the manufacture of viscose products, such as filaments, sheets and the like, and has for its object the removal of discoloration caused by the inclusion of heavy proachesclosely in whiteness a strongly bleached product.

During the manufactureof rayon-by the viscose process, the acid. of the precipitating bath and the sulfides liberated from the decomposed viscose solution in the precipitating bath may react with heavy metals or salts, metallic impuritiesin the bath or viscose solutions, or with various surface-active agents present in the bath to form tiny insoluble particles which adhere to the freshly coagulated filaments, thereby imparting a discoloration which is not removed by ordinary washing, desulfuring, or bleaching without physically damaging the yarn. I

It is the object of the present invention to remove these impurities and the-attendant discoloration from viscoseproducts' during the purification process without deleteriously afiecting the physical characteristics and without materially increasing the time or labor required for ordinary purification. I have discovered that the aforementioned discoloration may be removed by treating the coagulated and at least partly regenerated cellulose, preferably while in its gel state, with a metaphosphate, a tetraphosphataor a polyphosphat-e- I have found the hexametaphosphate and metaphosphoric'acid to be especially efiective when used in anacid medium which is at least pH 3 or more strongly acid, for example at pH 2.7. My invention, accordingly, provides a method for removing the discoloration from a viscose product by subjecting the product to an acid removal washing operation with a dilute aqueous solution of a metaphosphate, especially of an alkali metal hexametaphosphate, like sodium hexametaphosphate.

The removal of the discoloration may be effected by the addition of a small quantity of an alkali metal hexametaphosphate, for example, from 0.025% to 0.1% based on the water, to one or more portions of the wash water used for removal of acid and other impurities from the freshly formed viscose product, for example, filaments or yarn. The invention is advantageously carried out at the earliestpossible time in the washing schedule while the pH is-low,=that is, while the cellulose isstillacid, with a diluteaqueous solution of the-metaphosphate, at a tempera-.-

ture around 50 C. to 69 C. The washing treatiment of the "invention is preferably carried out ent wash water.

while theyarn is in the gel state.

The exact chemical nature of the'contaminants causing the"'discoloration which the metaphos phates are capable of removing in accordance 1 with the invention is not fullykn'own at-the present time. However, certain of the impurities or contaminants include metallic salts and sulfides, such as'lead'and antimony saltsand sulfides. It is conceivable that many kinds'of impurities or contaminantsmaybe present in'so complex a system. Suffice it to saythe greater part of the impurities causing the aforementioned discoloration is removed by the method of the invention.

In carrying'outa method of the invention for the removal of the discoloration appearing in freshly coagulated viscose filaments during the spinning process, the discoloration removal may be efiected during the purification phase of the manufacturing process without additional purification time or yarn handling being required and with only a slight increase in cost. No deleterious effects on the physicalcharacteristics of the resulting yarn occurs and the whiteness of some types of yarn so treatedcompare favorably with well bleached commercialyarns now being marketed.

The alkali-metal metaphosphate may beobtained in commercially available forms, for examzple, as sodium hexametaphosphate. The glassy sodium phosphate, sometimes called Grahams salt, is an effective form of metaphosphate.

Suitable forms of material which may be used in the treatment of the invention are marketed under the trade names Buromin, Sofos, Solium viscose filaments, evaluation measurements were made by means of a- General Electric Recording Spectrophotometer. The results of the invention will, accordingly, be better understood with reference to Figs. 1 and 2 which are composite reproductions of the recordings of the Spectrophotometer.

The following are examples illustrative 'of the methodof the invention:

Example 1 A freshly spun, unwashed cake 0f viscose yarn on a foraminated aluminum bobbin was placed in a smallwashing unit equipped with an evacuation apparatus and means of collecting the effiu- The vacuum sealwas effected by means of a rubber-gasketed fitting below and a rubber-gasketed cap above the bobbin.

The tub was filled with Wash water at 60 C. to which 0.1 of sodium hexametaphosphate had been added. A vacuum of 20 in. mercury was drawn and washing continued for 50 minutes, the bath level, temperature, and concentration being maintained by intermittent or continuous additions.

At the termination of this period, the bath was drained and replaced by hot water and all subsequent washing, desulfuring, drying and testing were carried out. The whiteness of the resulting yarn was greatly improved with respect to yarn made from the same viscose and not given the treatment of the invention. The physical characteristics of the yarn were unimpaired.

Example 2 A repeat of Example 1 except the hexametaphosphate was used for two successive 50-minute periods replacing equal wash-water periods. The resulting yarn was even whiter than that of Example 1 and compared favorably with commercially bleached yarn.

Example 3 A repeat of Example 2 without draining bath and refilling between periods. Results were virtually the same as in Example 2.

Example 4 A repeat of Example 2 using 0.05% of the hexametaphosphate. The resulting yarn was comparabl in whiteness to that of Example 1.

Example 5 A repeat of Example 4 except the hexametaphosphate was used for four successive (2 addition) 50-minute periods. The results were excellent. The yarn whiteness compared favorably with commercially bleached yarn. No loss in physical characteristics was encountered in this yarn or in any of the yarns given the hexametaphosphate treatment.

Example 6 A repeat of Example 2 except the temperature of the first bath was 30 C. instead of 60 C. The results were inferior to those at higher temperatures but were still far superior to the control yarn washed without the hexametaphosphate.

Example 7 A repeat of Example 6 except 50 C. baths replaced the 60 C. baths. The resulting color improvement was not quite as great as in Example 6 but was quite acceptable.

Example 8 A repeat of Example 2 except metaphosphoric acid was substituted for sodium hexametaphosphate. The resulting improvement in yarn whiteness was considered good, but did not equal that obtained in Example 2.

Example 9 Freshly spun, unwashed cakes of viscose yarn (150/40 Bright) on aluminum bobbins were placed in a vacuum washing unit. Vacuum seals were effected by means of rubber-gasketed fittings and cap.

The unit was filled with water at 60 C. to which 0.1% of sodium hexametaphosphate had been added. A vacuum of 20-25 inches of mercury was applied and vacuum washing continued for Washing Schedule for Natural Color Washing Schedule of Invention Min.-Water30 C. 200 Min.Water--60 C. 200 Min.-Water-60 C.

400 Min.--( )60 C. Min.Water-60 O. Min.Water-60 O.

1 0.05% sodium hexametaphosphate.

The parn was thereafter treated with a desulfurizing solution, rinsed and dried in accordance with conventional practice. The yarn package had the following characteristics:

Weight of yarn (dry basis) pound 1 Thickness of yarn cake mm 19 Length of package-outside mm 130 Length of package-inside mm Rate of flow gal./min 0.01

Fig. 1 shows quantitative reflection factors in terms of magnesium oxide for the visible spectrum of the normal natural color yarn, the same yarn subjected to a sodium hexametaphosphate treatment as in Example 9, and a highly bleached commercial yarn, as determined with the General Electric Recording Spectrophotometer.

Example 10 Freshly spun, unwashed cakes of viscose yarn (150/40 Bright) on aluminum bobbins were treated similar to those of Example 9 except the wash water was used at 50 C. and contained the same concentrations of sodium hexametaphosphate. The solution in the tub was drained after the first 50 minutes then refilled with a 0.05% solution of sodium hexametaphosphate. This drainage was desirable to remove the soluble impurities diffused out of the yarn cake into the wash water. The purification was continued as per the schedule below. Regular natural color yarn was washed without the hexametaphosphate treatment and used as a control. The comparative purification schedules are listed in the following table:

[150/40 Bright.]

Hexametaphosphate Treatment Natural Color Invention 50 Min.( )50 C. 200 Min.( )-50 C. 100 Min.-Watci-50 C.

350 Min.Water-50 C.

1 0.05% sodium hexametaphosphate.

The yarn was thereafter treated with a desulfurizing solution, rinsed and dried in accordance with conventional practice. The yarn package had the following characteristics:

Weight of yarn (dry basis) pound 1 Thickness of yarn cake mm 19 Length of packageoutside mm 130 Length of package-inside mm 180 Rate of flow gal./min 0.01

asst-mar:

' Fig. 1 2 shows the-effect oi? 1 the hexametaphosphate treatment of Example 10. superimposition of the graphs shows that reflection factors of this yarn treated according to the invention approximate thoseof curve 2. The color improvement isstriking in comparison withthe two well bleached commercial yarns.

Iclaim:

1. In a method for the removal of discoloration offreshly formed viscose products coagulated in an acid bath, the improvement which comprises washing the formed viscose product while it is'still acid with an aqueoussolution of 'a polyphosphate, the washing solution, containing the viscoseproductto'be washed, having apH below-pHB at the beginning of the washing step.

2. In a method for the removal of discoloration'of freshly formed viscose products coagulated in an acid'bath, the improvement which comprises washing the formed viscose'product while it is still acid and while it is in its gel state with an aqueous solution of a polyphosphate, the washing solution, containing the viscose-product'to be washed, having a pH below pH3 at the beginning of the washing step.

3. In a method for the removal of discoloration of freshly formed viscose products coagulated in an acid bath, the improvement which comprises washingthe formed viscose product while it is still acid with an aqueous solution of a metaphosphate, the washing solution, containing the viscose product to be washed, having a pH below pH3 at the beginning of the washing step.

4. In a method for the removal of discoloration of freshly formed viscose products coagulated in an acid bath, the improvement which comprises washing the formed viscose product while it is still acid with an aqueous solution of a metaphosphate, the washing solution, containing the viscose product to be washed, having a pH below pI-I3 at the beginning of the washing step, said solution being at a temperature of around 60 C.

5. In a method for the removal of discoloration of freshly formed viscose products coagulated in an acid bath, the improvement which comprises washing the formed viscose product while it is still acid with an aqueous solution of an alkali metal hexametaphosphate, the washing solution, containing the viscose product to be washed, having a pH below pH3 at the beginning of the washing step, said solution being at a temperature at least 50 C.

6. In a method for the removal of discoloration of freshly formed viscose products coagulated in an acid bath, the improvement which comprises washing the formed viscose product while it is still acid with an aqueous solution containing an alkali metal hexametaphosphate in an amount varying from 0.025% to 0.1% by weight, said solution having a pH below pH2.7 during at least part of the washing operation.

'2. In a method for the removal of discoloration of freshly formed viscose products coagulated in an acid bath, the improvement which comprises washing the formed viscose product while it is still acid with an aqueous solution of a metaphosphoric acid, the washing solution, containing the viscose product to be washed, having a pH below pI-I3 at the beginning of the washing step.

8. In a method for the removal of discoloration of freshly formed viscose products coagu- 8" 1ated in=an acid bath, the improvement which compriSeS treating the formedviscose product whi-leit' is 'still acid with an aqueous solution' of sodium hexametaphosphate at a temperature "of 50 C. to 60 C. forat' least part of the-purification period, said washing solution, containing'the viscose productto be washed, having apH below pH3 at the beginning of thewashing step.

9. In a method for the removal of discolorationof freshly formed viscose products coagulated in an acid bath, the improvement'which comprises treating the formed viscose product while it is still acid with-an aqueous solution of apolymetaphosphate at atemperature of 50 C.

to60 Cufor at least part of the purification period, said washing solution, containing the viscoseproduct to be washed, having a pH below pH3 at the beginning of the washing step.

10. In a method for the removal of discoloration of freshly formed viscose products coagulated in an acid bath, the improvement which comprises treating the formedviscos'e product while it is still acid-with an aqueous solution of a'polyphosphate at a temperature of 50C. to 60 C.-for at leastpart of the purification period, said "washing solution, containing the viscose product to be washed, having a pH below pH3 at the beginning of the washing step.

11. In a method of manufacturing filaments or films from viscose wherein viscose is extruded into and coagulated by a bath containing acid and the freshly formed viscose product is subsequently purified by a sequence of steps comprising washing the product to remove entrained and occluded acid coagulating bath, treating with desulfurizing solution to remove liberated sulfur and rinsing with water to remove the adherent desulfurizing solution, the improvement which consists in employing Water containing sodium hexametaphosphate as the medium for washing the product to remove the entrained and occluded acid coagulating bath so as to effect the removal of discoloration from the said freshly formed viscose product.

12. In a method of manufacturing filaments or films from viscose wherein viscose is extruded into and coagulated by a bath containing acid and the freshly formed viscose product is subsequently purified by a sequence of steps comprising washing the product to remove entrained and occluded acid coagulating bath, treating with desulfurizing solution to remove liberated sulfur and rinsing with water to remove the adherent desulfurizing solution, the improvement which consists in employing water containing sodium hexametaphosphate and having an initial pH below pI-I3 as the medium for washing the product to remove the entrained and occluded acid coagulating bath so as to effect the removal of discoloration from the said freshly formed viscose product.

13. In the production of regenerated cellulose products the step comprising subjecting the freshly regenerated cellulose product to a solution of a salt of the group consisting of polyphosphates and metaphosphates.

14. In the production of regenerated cellulose products the step comprising subjecting the freshly regenerated cellulose product to a solution of an alkali metal salt of hexametaphosphate.

15. In the production of regenerated cellulose products the step comprising subjecting the freshly regenerated cellulose product to a solution of sodium hexametaphosphate.

16. In the production of regenerated cellulose products the step comprising subjecting the freshly regenerated cellulose product to a solution of sodium hexametaphosphate having a concentration between .05% and .1

17. In the production of regenerated cellulose products the step comprising subjecting the freshly regenerated cellulose product while wet with acid coagulating bath to a solution of a salt of the group consisting of polyphosphates and metaphosphates.

18. In the production of regenerated cellulose products the step comprising subjecting the freshly regenerated cellulose product while wet with acid coagulatin bath to a solution of an alkali metal salt of hexametaphosphate.

19. In the production of regenerated cellulose products the step comprising subjecting the freshly regenerated cellulose product while wet with acid coagulating bath to a solution of sodium hexametaphospha-te.

20. In the production of regenerated cellulose products the step comprising subjecting the freshly regenerated cellulose product while wet with acid coagulating bath to a solution of sodium hexametaphosphate having a concentration between 0.025 and 0.1

HERMAN JOSEPH LESSER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,576,530 Mendel Mar. 16, 1926 1,580,843 Mendel Apr. 13, 1926 1,604,889 Dreaper Oct. 26, 1926 1,633,220 Mendel June 21, 1927 1,655,097 Gladding -1 Jan. 3, 1928 1,977,533 Thurmond Oct. 16, 1934 2,031,827 Fiske Feb. 25, 1936 2,066,371 Stein Jan. 5, 1937 2,092,203 Brennecke Sept. 7, 1937 2,140,008 Hall Dec. 13, 1938 2,374,100 Jackson Apr. 17, 1945 FOREIGN PATENTS Number Country Date 443,498 Great Britain 1935 191,212 Switzerland Aug. 16, 1937 

1. IN A METHOD FOR THE REMOVAL OF DISCOLORATION OF FRESHLY FORMED VISCOSE PRODUCTS COAGULATED IN AN ACID BATH, THE IMPROVEMENT WHICH COMPRISES WASHING THE FORMED VISCOSE PRODUCT WHILE IT IS STILL ACID WITH AN AQUEOUS SOLUTION OF A POLYPHOSPHATE, THE WASHING SOLUTION, CONTAINING THE VISCOSE PRODUCT TO BE WASHED, HAVING A PH BELOW PH3 AT THE BEGINNING OF THE WASHING STEP. 